This application claims priority of Japan patent Application No. 2000-024082, filed on Feb. 1, 2000.
1. Field of the Invention
This invention relates to a structure of a polishing head of a polishing apparatus of a semiconductor wafer by CMP (Chemical Mechanical Polishing) and, more particularly, to a structure of a polishing head floating on air while polishing a wafer.
2. Description of the Related Art
As processing of ICs has made progress in recent years, the formation of IC patterns in multiple layers has been conducted. In this case, the occurrence of surface unevenness is unavoidable to a certain extent. It has been customary to form, as such, a pattern of a next layer on a preceding layer. As the number of the layers increases, however, the widths of lines and the diameters of holes have become smaller. The smaller the dimension, the more difficult it becomes to form an excellent pattern with the result that defects are more likely to occur. Therefore, it has been customary to polish the surface of a preceding layer on which the pattern is formed, so as to planarize the surface, and then to form the pattern of a next layer. To polish a wafer during the formation process of the IC pattern, a wafer polishing apparatus (CMP apparatus) using a CMP method has been employed.
An ordinary wafer polishing apparatus includes a disc-like polishing table having a polishing pad bonded to a surface thereof, a plurality of wafer polishing heads for holding one of the surfaces of a wafer to be polished and bringing the other surface of the wafer into contact with the polishing pad, and a head driving mechanism for causing these wafer polishing heads to rotate relative to the polishing table. Polishing is conducted while a slurry of a polishing agent is supplied between the polishing pad and the wafer.
A mechanism in which a packing material (wafer bonding sheet) is bonded to a wafer-holding carrier on a carrier surface side to be pushed, and one of the surfaces of the wafer is bonded to, and held by, this packing material (Japanese Unexamined Patent Publication (Kokai) No. 8-229808), and a mechanism in which a resilient porometic polyurethane insert is bonded to a carrier and the wafer is bonded to, and held by, this insert (Japanese Unexamined Patent Publication (Kokai) No. 6-79618) are known as the wafer holding mechanism of the wafer polishing heads.
In the conventional wafer holding mechanisms described above, however, a so-called xe2x80x9cpacking sheetxe2x80x9d must be bonded to the surface of the carrier. However, air bubbles are likely to develop when the packing sheet is bonded, and skill is necessary for the bonding work. Planarity of the packing sheet bonding surface of the carrier and variance of the thickness of the packing material affect a wafer-processing surface. Furthermore, the wafer polishing heads must be removed whenever the packing sheet is bonded.
To solve these problems, the applicant of the present invention previously proposed a wafer polishing apparatus in Japanese Patent Application No. 10-92030. This wafer polishing apparatus employs an air blast member disposed on the lower surface of a carrier idly supported inside a wafer holding head main body in such a manner as to be capable of moving up and down, for blowing air to the rear surface of the wafer to form a pressure fluid layer between the carrier and the wafer. The wafer is pushed to a polishing table through this pressure fluid layer and is held.
Nonetheless, this wafer holding mechanism of the wafer polishing apparatus is not yet free from the problem that the rear surface of the wafer is likely to come into direct contact with, and to be damaged by, a hard surface of the carrier during delivery of the wafer by adsorption and during its polishing.
Therefore, the applicant of the present invention further proposed a wafer polishing apparatus in Japanese Patent Application No. 11-128558. In this wafer polishing apparatus, a protective sheet is disposed on an outer surface of an air blast member on a lower surface of a carrier, and is used as an air bag that is inflated by air from the air blast member so as to push the wafer to a polishing pad.
In this air bag system, an exhaust port for the air remains constant. Therefore, when the air pressure inside the protective sheet becomes higher than the pushing force that pushes the carrier and a retainer ring, a force that tilts the carrier develops if the point of receiving a lateral force exists above the surface of the polishing pad during processing, and this force affects processing accuracy. In addition, a variation in the thickness of the surface shape of the sheet affects processing accuracy, too.
It is an object of the present invention to provide a structure of a polishing head of a wafer polishing apparatus that completely inhibits jump-out of a wafer from inside a polishing head during polishing, and also inhibits undulation of a polishing pad and variance of thickness of a packing material (rubber sheet) from affecting planarization accuracy.
In a structure of a polishing head of a wafer polishing apparatus according to the present invention, a rubber sheet is disposed on an inner surface of a retainer ring, an air bag is formed by air from an air blast port of a carrier, and an upper outer peripheral edge of a carrier, that protrudes from the carrier, is placed on the retainer ring to form a seal portion of air. Therefore, even when a retainer pressure for pushing the retainer ring to the polishing pad is set to a low pressure and an air bag pressure for pushing the wafer is set to a high pressure, the seal portion plays the role of a regulator valve and the carrier does not push the wafer out from the retainer ring. The pushing force of the wafer does not change against the lateral force during processing of the wafer. Furthermore, the wafer is not damaged by coming into contact with the hard surface of the carrier.
In a structure of a polishing head according to another embodiment of the present invention, a plurality of holes is formed in the rubber sheet. In this way, the wafer adsorption holding effect of the polishing head during transportation of the wafer can be improved, and air blown out from the holes of the rubber sheet pushes the wafer to the polishing pad during polishing. Therefore, variation of the thickness of the rubber sheet and undulation of the polishing pad do not affect processing accuracy of the wafer. Since the quantity of air blown out from the gap between the wafer and the rubber sheet is extremely small, aggregation of slurry does not occur.
In a structure of a polishing head according to still another embodiment of the present invention, an interconnection portion constituting a retainer ring and a retainer main body are connected to each other by a ring so that assembly and disassembly can be done easily.
In a structure of a polishing head according to still another embodiment of the present invention, an exchange portion constituting the retainer ring is removably fitted to the retainer main body and the rubber sheet is clamped between the exchange portion and the retainer main body. In consequence, the exchange portion that undergoes wear can be frequently exchanged, and the rubber sheet, too, can be exchanged easily.
In a structure of a polishing head according to still another embodiment of the present invention, a lower surface of the carrier is divided into a plurality of regions, and a second rubber sheet is further disposed so that an air bag can be formed in each of these regions. As a result, the wafer processing quantity can be changed depending on the regions.
The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.